JP2012527597A - Oxygen combustion steam generator - Google Patents

Abstract

In the operation method of the steam generator, a transport reactor is provided. Only a substantially pure oxygen feed stream having an amount sufficient to maintain the transport reactor above a particular system load is introduced into the transport reactor. This particular load is the system load when only a substantially pure oxygen feed stream is provided to the transport reactor at the minimum flow rate for operating the transport reactor. The fuel is combusted in the presence of this substantially pure oxygen feed stream to produce flue gas containing solid material. The solid material is separated from the flue gas and transferred to a heat exchanger. This heat exchanger can be one of a moving bed heat exchanger or a fluidized bed heat exchanger. The solid material is introduced into the transport reactor and contributes to the combustion process.
[Selection] Figure 1

Description

  The specification described herein relates generally to a steam generator, and more specifically to a steam generator in which substantially pure oxygen is supplied to a transport reactor.

  Steam generators, particularly coal combustion type steam generators, can produce harmful emissions. Recent efforts have focused on oxyfuel combustion, which produces essentially pure carbon dioxide product gas that can be more efficiently sequestered by removing the nitrogen produced by air combustion. Many oxyfuel steam generators utilize gas recirculation significantly to maintain the required flow rate within the steam generator, thereby supporting the heat exchange process. High-speed gas recirculation introduces considerable cost and complexity and increases the need for an auxiliary power source.

  The pulverized coal steam generator relies on the area of the furnace to control heat exchange. These systems also inherently require substantial gas recirculation to maintain the furnace and convection surface velocity.

  In one embodiment, in the method of operating the steam generator, a transport reactor is used, and the substantially pure oxygen feed stream is only the external feed gas, which is the flow rate in the reactor. Is introduced during the combustion process in an amount sufficient to raise the desired flow rate above the minimum threshold flow rate. Thus, the amount of substantially pure oxygen added will vary depending on the flow rate desired in the transport reactor. The term “substantially pure oxygen” as used herein should be taken to mean a gas containing 95 to 100% oxygen. During operation, when the transport reactor is operating at substantially full load, fuel and substantially pure oxygen are combusted to produce flue gas with ash and other hot solids that form part of it. To do. After combustion, the flue gas is separated into a final product portion and a recycle product portion. The recycle product portion passes through a moving bed or fluidized bed type heat exchanger. Heat from the hot flue gas is transferred to a working fluid that forms part of a heat exchanger such as, but not limited to, water, steam or steam. The recycle product portion is then sent to the transport reactor to contribute to the combustion process.

  In one embodiment, the separator is a cyclone and the transport reactor operates at a flow rate between about 30 feet / second and about 50 feet / second. In this embodiment, the heat exchanger is a moving bed heat exchanger (MBHE) in fluid communication with the outlet of the separator. The moving bed heat exchanger has a bypass that diverts a portion of the recirculated product portion to a cylindrical heat exchanger that forms part of the MBHE, and converts the hot combustion product to the heat exchanger. More advanced temperature control is performed in the transport reactor by diverting it back to the transport reactor. Further, the transport reactor has an inlet, and supplementary air and supplemental inert gas pass through the inlet and are introduced into the transport reactor. Supplementary air or supplemental inert gas is introduced when the flow rate in the reactor is below the minimum threshold level. By adding make-up air or make-up inert gas, the flow rate in the transport reactor is increased to at least the threshold speed to the point where substantially pure oxygen can be introduced.

  Also, a steam generator will be described. This steam generator has a transport reactor with an outlet and an inlet defined. A separator is provided, the separator having an inlet in fluid communication with the transport reactor outlet, at which the generated flue gas is received and defined by the separator. A final product portion that passes through one outlet and a recycle product portion that passes through a second outlet defined by a separator. The MBHE or fluidized bed heat exchanger is located downstream from the second outlet of the separator and has an inlet in fluid communication with the outlet. The heat exchanger also has an outlet in fluid communication with the inlet of the transport reactor. The transport reactor has an inlet through which make-up air and make-up inert gas are provided to maintain the transport reactor throughput under conditions of substantially less than full load. Once substantially full load conditions have been achieved, the addition of make-up air or make-up inert gas is not continued, and at this point only substantially pure oxygen can be supplied to the transport reactor. When operating at substantially full load, substantially pure oxygen is the only gas supplied from the outside to the transport reactor.

  In certain embodiments, the substantially pure oxygen feed stream passes through an oxygen preheater located downstream of the first outlet of the separator before entering the transport reactor. Because the oxygen preheater is in fluid communication with the final product portion and the substantially pure oxygen feed stream, heat is transferred from the final product portion of the flue gas to the substantially pure oxygen feed stream.

  These and other features are exemplified by the following drawings and detailed description.

  Here, the same numbers are given to similar elements, and the drawings which are exemplary embodiments are referred to.

It is the schematic of the steam generator which uses a moving bed heat exchanger.

It is the schematic of the steam generator using a fluidized bed heat exchanger.

  As shown in FIG. 1, the transport reactor, schematically designated by reference numeral 10, operates as a combustor and defines an inlet 12 and an outlet 14. Without limitation, a solid fuel 64 such as coal is fed to the transport reactor. When the transport reactor 10 is operating at a particular system load or above, substantially all transport gas is supplied by conduits 16 and 48. This particular system load definition is defined by the conditions when all or substantially all of the transport gas is supplied by conduits 16 and 48 at the minimum flow rate at which the transport reactor 10 operates. This minimum flow rate is defined by the structure and parameters of the transport reactor and solid fuel, such as the dimensions of the transport reactor and solid fuel. Some or substantially all of the transport gas may be heated in an oxygen preheater 18 (described in detail below) before being supplied to the combustor. Combustor outlet 14 is connected to inlet 20 of separator 22 via conduit 24. As shown in the illustrated embodiment, the separator 22 includes an upper outlet 26 for releasing the final product portion of the flue gas, and heated solids that have not been consumed in the residue in the combustor 10 as well as combustion. A cyclone having a lower outlet 28 for releasing a recycle product portion of the flue gas containing ash generated during processing. The lower outlet 28 of the cyclone 22 is described in detail below as a “moving bed heat exchanger (MBHE)” and is in fluid communication with the inlet 29 of the heat exchanger 30 shown in the illustrated embodiment. Has been. Although MBHE is illustrated, the present invention is not limited thereto, for example, a book such as a “Fluidized Bed Heat Exchanger (FBHE)” shown in FIG. 2 and described in detail below but not limited thereto. Other types of heat exchangers known to those skilled in the relevant field to which the invention relates can be used instead.

  The transport gas flowing through conduits 16 and 18 is a substantially pure oxygen supply stream that is substantially pure oxygen supplied by oxygen source 46, heat exchanger 30, solid fuel. It consists of the source and / or any other residual gas that would come from the oxygen preheater 18. The substantially pure oxygen supply stream is comprised of approximately 90 to 100% oxygen. As suggested, adding a fluidizing gas, such as air, to the heat exchanger that forms part of the embodiments described herein will substantially reduce the oxygen purity of the pure oxygen feed stream. Influence. Although air has been described as a fluidizing gas for a heat exchanger, the present invention is not limited thereto, and other gases such as, but not limited to, flue gas and substantially pure oxygen can also be used.

  Still referring to FIG. 1, the make-up gas line 31 is connected to an inlet 27 to the transport reactor 10. In operation, if the transport reactor 10 is operating at a desired system load below the minimum flow rate, make-up air or inert gas to increase the flow rate in the transport reactor to at least the minimum flow rate. For example, but not limited to, a gas such as combustion exhaust gas can be introduced into the transport reactor via the gas line 31. At this time, a substantially pure oxygen feed stream can be introduced into the transport reactor. The substantially pure oxygen feed flow introduced into the transport reactor will be governed by the desired system load within the transport reactor.

  The outlet 32 of the MBHE 30 is in fluid communication with the conduit 16 so that the recycle product portion described above passes through the MBHE and then is supplied with a substantially pure oxygen feed stream and fuel supplied into the conduit. It is mixed and conveyed into the combustor 10 via the combustor inlet 12.

  The final product portion of the flue gas is exhausted from the cyclone 22 via the upper outlet 26 and is defined by a backpass duct 35 as a backpass volume. ) Flows into 33. The heat exchanger 34 is in communication with the backpass duct 35 and uses a working fluid such as steam, water or steam supplied through tubes and / or coils that form part of the heat exchanger. Yes. The hot end product portion of the flue gas is conducted and convectively passed through the heat exchanger 34 to heat the working fluid to the desired temperature.

  After the final product portion of the flue gas has passed through the backpass volume 33, this final product portion flows into the oxygen preheater 18, as will be described in more detail below, for substantially pure oxygen. Pre-heating before introduction into the combustor 10.

  As described above, the lower outlet 28 of the cyclone 22 is in fluid communication with the MBHE 30. The MBHE 30 defines an inner region 40 into which the recirculation product portion of the combustion exhaust gas flows after being discharged from the lower cyclone outlet 28. The MBHE 30 is a countercurrent direct contact heat exchanger employing a solid mass flow moving downstream through a series of cylindrical heat exchangers 42. For example, but not limited to, heat from the combustion products is transferred to a cylindrical heat exchanger to heat a working fluid, such as steam, to a desired processing temperature. In the cylindrical heat exchanger 42, fins can be used to increase the heat transfer area. The heat transfer mechanism of MBHE 30 is characterized by conduction and convection with a higher heat transfer rate than that achieved using gas-only convection. Although the MBHE 30 has been described as a countercurrent direct contact heat exchanger, the MBHE 30 is not limited to this, and the heat exchanger can also be constructed of a parallel flow type.

  The MBHE 30 shown in the illustrated embodiment includes a bypass 44 for diverting some of the recycle product portion of the flue gas to the cylindrical heat exchanger 42. As a result, a part of the high-temperature combustion product is diverted to the heat exchanger and returned to the combustor, whereby more advanced temperature control is performed in the combustor 10.

  During operation of the transport reactor 10 above a particular system load, the substantially pure oxygen feed stream can be all or substantially all of the gas introduced into the transport reactor. By using substantially pure oxygen in this way, combustors as high as over 80% compared to air-fired “circulating fluidized bed (CFB)” and due to their low gas weight and higher combustion rate and In some cases, a dramatic reduction in furnace area may be possible. In addition, gas recirculation is not used, and instead the discharge pressure of oxygen source 46 (described below) that supplies substantially pure oxygen to conduit 16 operates as the main draft source.

  Substantially pure oxygen is supplied from the oxygen source 46 to the transport reactor 10 via the oxygen introduction element 48. Substantially pure oxygen supplied from the oxygen source 46 is preheated by the oxygen preheater 18 upstream of the oxygen introduction element 48. The oxygen preheater 18 has a cold side inlet 50 that communicates with an outlet 52 defined by an oxygen source 46. The oxygen preheater 18 has an oxygen outlet 54 in fluid communication with the oxygen inlet element 48 to introduce heated substantially pure oxygen into the oxygen inlet element 48. The final product portion of the flue gas supplied from the backpass volume 33 passes through a conduit 56 that communicates with the high temperature side inlet 58 of the oxygen preheater.

  Substantially pure oxygen supplied by the oxygen source 46 may be generated by an air separation unit that separates oxygen from the ambient air stream. Therefore, the oxygen source 46 may be constituted by a low temperature plant. The oxygen source 46 may be configured as a device including an oxygen transport film.

  As shown in FIG. 1, a mechanism 62 for capturing combustion process by-products such as, but not limited to, particulates and sulfur dioxide is located downstream of the oxygen preheater 18 and, in the illustrated embodiment, a conduit. 56.

  The combustor 10 shown in the illustrated embodiment is a transport reactor, and the flow rates of combustion gases and solids (ash and unconsumed fuel) are preferably between about 30 feet / second and about 50 feet / second. Between. However, the present invention is not so limited, as any effective flow rate known to the relevant technicians to which the present invention pertains can be used.

The transport reactor 10 operates at a higher temperature than conventional reactors. Typically, the transport reactor is operated at a temperature just below the ash melting temperature of the fuel used. This temperature is typically about 2000 ° F., but may vary somewhat depending on the fuel supplied to the combustor. Due to these high operating temperatures, N ₂ O is typically destroyed and is not a byproduct of the combustion process. However, NO _X is generated during the combustion process. Thus, the selective catalytic reactants (SCR) 60, disposed downstream of the bypass duct 33 of the heat exchanger 34 to remove the NO _X from the final product portion of the flue gas. A capture mechanism 62 is disposed downstream of the oxygen preheater 18 for capturing sulfur dioxide (SO ₂ ) and fine particles present in the combustion exhaust gas. In the illustrated embodiment, the capture mechanism is in communication with the conduit 56.

  Still referring to FIG. 1, an induced draft (ID) fan 65 may be provided if desired.

  Referring to FIG. 2, the embodiment shown here is similar to the embodiment shown in FIG. Therefore, the same number with 1 at the head is given to the same element. 2 differs from the embodiment shown in FIG. 1 in that the system of FIG. 2 uses a fluidized bed heat exchanger (FBHE) 130 and a throttle valve 131 instead of MBHE 30. It is a point. The FBHE 130 shown in the illustrated embodiment uses a bypass 144. Bypass 144 has a first outlet 164 in fluid communication with conduit 145 in fluid communication with the opposite side of conduit 116, and a second outlet 166 in fluid communication with throttle valve 131. Throttle valve 136 is also in fluid communication with conduit 116 so that during operation, the throttle valve operates to return some of the hot combustion products back to combustor 110, so that the combustor The temperature in 110 is controlled.

  The FBHE 130 is in gaseous communication with the fluidizing gas supply line 168. By using supply line 168, fluidized gas such as, but not limited to, air, flue gas or substantially pure oxygen is introduced into fluidized bed 170 forming part of FBHE.

  The embodiment described herein uses supplying substantially pure oxygen to the transport reactor 10. An advantage of configuring the steam generator in this way is that it reduces the complexity of the steam generator. The low gas weight and higher combustion rate can significantly reduce the combustion furnace area required by conventional air-fired CFB steam generators.

  In the embodiment described here, the combustion process and the heat transfer process are separated to allow more effective heat transfer in the heat exchanger.

  The invention has been described with reference to various exemplary embodiments. However, one of ordinary skill in the art appreciates that various modifications can be made and equivalent elements can be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to what is suggested in the present invention without departing from the essential scope thereof. Accordingly, the invention is not limited to the specific embodiments disclosed as the best mode contemplated for practicing the invention, but includes all embodiments that fall within the scope of the appended claims. Intended.

Claims (20)

A method for operating a steam generator,
Providing a transport reactor; and
Only a substantially pure oxygen feed stream having an amount sufficient to maintain the transport reactor above a specific system load is introduced into the transport reactor, and the specific system load refers to operating the transport reactor. A system load when only a substantially pure oxygen feed stream is fed to the transport reactor at a minimum flow rate to
Combusting fuel in the presence of the substantially pure oxygen supply stream to produce flue gas, the flue gas containing a solid material;
Separating the solid material from combustion exhaust gas;
Passing the solid material through a heat exchanger;
Introducing a solid material into the transport reactor to contribute to the combustion process. The method of claim 1, wherein
The method of claim 1, wherein the substantially pure oxygen feed stream comprises 90-100% oxygen. The method of claim 1, wherein
After separating the flue gas, the method further comprises passing the separated flue gas portion through an oxygen preheater that transfers heat from the flue gas to the substantially pure oxygen supply stream. Feature method. The method of claim 1, wherein
The method further comprises:
Providing an inlet to the transport reactor;
When the transport reactor is operating at a flow rate less than a minimum threshold flow rate, a supply of supplemental air and supplemental inert gas having an amount sufficient to increase the flow rate in the transport reactor to the minimum threshold flow rate. Supplying at least one to the inlet and allowing it to flow into the transport reactor. The method of claim 1, wherein
The heat exchanger is a fluidized bed heat exchanger;
The method further comprises:
Providing an inlet to the fluidized bed heat exchanger;
Introducing fluidized gas into the inlet of the fluidized bed heat exchanger through the inlet. The method of claim 5, wherein
The fluidized gas is at least one of flue gas, air, and substantially pure oxygen. The method of claim 1, wherein
The heat exchanger is one of a moving bed heat exchanger and a fluidized bed heat exchanger, these heat exchangers having a bypass for passing at least a portion of the solid material;
The method further comprises the step of controlling the temperature in the transport reactor by operating the bypass. The method of claim 1, wherein
The separator is a cyclone;
The method further includes at least one heat exchange that communicates the separated flue gas portion of the flue gas after the separation and before passing the separated flue gas product portion through the oxygen preheater. Introducing the heat into the back path volume having a heater and transferring heat from the separated flue gas portion to the working fluid flowing in the one heat exchanger. The method of claim 1, wherein
The transport reactor is operated at a flow rate between about 30 feet / second and about 50 feet / second. The method of claim 7, wherein
The heat exchanger is a fluidized bed heat exchanger;
The method
Providing a throttle valve in fluid communication with the bypass and the heat exchanger;
Operating the throttle valve to control the flow rate at which the solid material is introduced into the transport reactor to control the temperature in the transport reactor. The method of claim 1, wherein
The method wherein the transport reactor is operated at a temperature proximate to an ash melting temperature defined by the fuel upon combustion of the fuel. The method of claim 1, wherein
The method of claim 1, wherein the substantially pure oxygen supply stream comprises 95 to 100% oxygen. The method of claim 1, wherein
The method according to claim 1, wherein the heat exchanger is one of a moving bed heat exchanger. A method for operating a steam generator,
Providing a transport reactor; and
Introducing only a substantially pure oxygen feed stream into the transport reactor having an amount sufficient to maintain a desired flow rate above the minimum threshold flow rate in the transport reactor;
Combusting fuel in the presence of the substantially pure oxygen supply stream to produce flue gas, the flue gas being a solid material, at least part of which is hot ash;
Providing a cyclone having an inlet in fluid communication with an outlet defined in the transport reactor, and introducing the combustion exhaust gas into the cyclone;
Operating the cyclone to separate the flue gas into a final product portion and a recycle product portion;
Passing the recycled product portion comprising at least a portion of the hot ash through a moving bed heat exchanger in fluid communication with an outlet of the cyclone;
Passing the final product portion through an oxygen preheater in which heat from the flue gas is transferred to the oxygen feed stream;
Introducing the recirculated product portion into the combustor to contribute to the combustion process. The method of claim 11, wherein
The method of claim 1, wherein the substantially pure oxygen feed stream comprises 90-100% oxygen. The method of claim 12, wherein
The method further comprises:
Providing an inlet to the transport reactor;
When the transport reactor is operating below a minimum threshold flow rate, at least one of supplemental air and supplemental inert gas having an amount sufficient to increase the flow rate in the transport reactor to the minimum threshold flow rate Introducing to the inlet and supplying to the transport reactor. 15. The method of claim 14, wherein
The method
After the flue gas separation and before passing the final product portion through the oxygen preheater, the final product portion of the flue gas is introduced into a backpass volume in communication with at least one heat exchanger, A method comprising the step of transferring heat from a final product portion to a working fluid flowing in said at least one heat exchanger. The method of claim 11, wherein
When the transport reactor is operating at substantially full load, the introduction of a substantially pure oxygen feed stream into the transport reactor causes the substantially pure oxygen feed stream to be the main source for the steam generator. A process wherein the substantially pure oxygen feed stream is introduced into the transport reactor at a sufficient flow rate and pressure to function as a draft source. The method of claim 12, wherein
The transport reactor is operated at a flow rate between about 30 feet / second and about 50 feet / second. A steam generator,
Combusting the fuel in the presence of only a substantially pure oxygen feed stream having an amount sufficient to maintain a desired flow rate above the minimum threshold flow rate in the transport reactor to produce a flue gas containing solid material The transport reactor;
An oxygen source supplying substantially pure oxygen;
A separator for separating the solid material from the flue gas;
And a heat exchanger that receives the solid material that is introduced into the transport reactor and contributes to a combustion process.

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